Cellular mobile radiotelephone systems are broken up into a plurality of serving cells each of which use a particular set of radiotelephone communication channel frequencies to communicate with mobile radiotelephones operating within the boundaries of the cell. Adjacent cells use different sets of radiotelephone communication channel frequencies to prevent interference between the communication channels of the serving cell and adjacent cells. When the mobile leaves a particular serving cell a handoff operation switches the existing established call from the serving cell (i.e. the source cell ) to a new target cell which becomes a new serving cell. This handoff process automatically changes the communication channel frequency from that of the original serving cell to a communication channel frequency of the target and subsequent serving cell.
A plurality of individual cells are normally grouped together and are connected to a mobile telephone switching office (MTSO) also sometimes designated as a mobile serving center (MSC), which interconnects the cells to a land line telephone system. Various MTSOs representing different systems are interconnected by land line trunks. As the mobile radiotelephone unit passes from one cell to another the resulting handoff process may connect the mobile radiotelephone unit to a different MTSO which is in turn connected, via a trunk line, to the MTSO of the original serving cell. If the mobile radiotelephone traverses a larger number of cells requiring a plurality of handoffs the inter MTSO trunk line connection may result in accumulation of a series of redundant MTSO inter trunk connections between the originating cell and the existing serving cell. Some of these trunk connections may overlaps, creating duplication of trunk connections, or may create an accumulation of a series of tandem trunk connections that are unnecessary and undesirable. These accumulative trunk and associated MTSO connections are known as tandem trunk connections and the related MTSO are known as tandem MTSOs. The tandem MTSO is defined as one involved in the call connection and handling, but it is neither a serving nor an originating MTSO.
The problem of accumulating tandem trunk connections as a result of successive handoffs has been addressed in a handoff limiting method disclosed in U.S. Pat. No. 4,398,063 (063) assigned to the assignee of this application. In a situation of successive handoffs, each successive serving MTSO maintains a list of the MTSOs previously involved in handling the call. The number of tandem connections resulting from the successive handoffs are reduced by having the serving MTSO determine if the target MTSO is already one of the previously included tandem connected MTSOs on the list of the MTSOs involved in handling the call but not directly serving the mobile radiotelephone. If the target MTSO is already in the chain of tandem connections, the existent serving MTSO initiates a drop back to that target MTSO so that all trunk connections in the chain of tandem connections completed subsequent to the present handoff to the now target MTSO are disconnected at the time that target MTSO assumes the role of the serving MTSO.
A large number of handoffs may result in an accumulation of tandem trunk connections involving a plurality of tandem MTSOs in which none of the accumulating target MTSOs has previously been operative as a serving MTSO. Frequently the travel route of the roaming mobile radiotelephone unit is such that the number of tandem MTSOs may be reduced due to availability of existing inter MTSO trunk connections, however the pattern of accumulation of tandem MTSOs is such that the aforementioned tandem MTSO reduction system is not operative to minimize tandem connections and reduce the number of tandem MTSOs.